ABSTRACT
This chapter begins with an introductory summary of basic properties of spin-polarised hydrogen. It discusses the properties of atomic quantum gases at ultra-low temperatures with atomic hydrogen as a primary example. Building on the extensive experience of various research groups with the low temperature gas phase of atomic hydrogen, many interesting aspects could be illustrated with well established experimental and theoretical results. As for many traps the single-particle motion is non-ergodic, interatomic collisions are usually essential to assure ‘sufficient ergodicity’. The chapter also discusses a number of thermodynamic properties relevant for the description of evaporative cooling using the truncated exponential energy distribution as a starting point. It considers the case of plain evaporative cooling. In forced evaporative cooling the escape threshold is lowered with decreasing temperature, thus allowing the evaporation to proceed at a desired rate.
